1. Field of the Invention
The invention relates to a totally insulated switched mode power supply.
2. Description of the Related Art
A totally insulated switched mode power supply that can be connected to a grounded AC or three-phase power supply system is generally known, where the switched mode power supply is provided for supplying a DC or AC voltage to a device or a load. This conventional switched mode power supply has Y capacitors, which are provided for asymmetrical interference suppression of the switched mode power supply or are acquired to meet the requirements in respect of the ENC response of the switched mode power supply. The two conductors in the switched mode power supply, where one conductor is connectable to the phase conductor and the connector is connectable to the neutral conductor via suitable connections, are wired symmetrically to a Y capacitor for this purpose to also avoid a relatively high voltage to the ground potential in cases in which the switched mode power supply is connected with incorrect polarity to the AC or three-phase power supply system. This means that a Y capacitor is connected between the phase conductor and the electrically conductive housing and a further Y capacitor is connected between the neutral conductor and this housing, where these capacitors have substantially the same capacitance.
Owing to the fact that the ground potential of the AC or three-phase power supply system, with the neutral conductor thereof being connected to this ground potential, is usually different than the potential of the housing, referred to below as frame potential, there is a voltage drop across the Y capacitor connected between the neutral conductor and the housing. In the case of a 220 V system voltage, in the most unfavorable case, a voltage of up to 110 V can drop across this Y capacitor, where a low current can flow from the frame to ground potential. In other words, the ground voltage allows a low fault current or leakage current to flow away via the always present leakage capacitance of a totally insulating or grounded device connected to the switched mode power supply or a “grounded” person.
This low fault current or leakage current, which is usually less than 5 mA, can cause unpleasant haptic stimuli in people and can also have a disruptive influence on sensitive electronic components of a device connected to the switched mode power supply or the peripheral interface thereof.